1. Field of the Invention
The present invention relates generally to printed circuit boards, and more particularly, to connecting printed circuit boards to other assemblies through connection systems.
2. State of the Art
Electronic and computer assemblies widely use board-to-board connector assemblies for coupling one board (e.g., daughter board) to a second board (e.g., motherboard) without requiring the use of separate cabling. One form of a common board-to-board connection system includes an edge connector and a socket connector coupled in a mating arrangement. For a printed circuit board application, each of the edge and socket connectors may be configured in an elongated arrangement with each including corresponding conductive contacts therealong. To facilitate an increasing number of interconnects on the respective boards, the length of the edge and socket connectors may increase until such a configuration reaches an unacceptable dimension.
One specific application of a board-to-board connection system includes the coupling of support or daughter boards with integrated circuits thereon with a motherboard. The connection system provides the electrical interface between additional accessible resources (e.g., memory resources) and a host system. The additional resources are formed by combining a printed circuit board with integrated circuits which form an electronic module. Specific electronic modules include memory modules when the integrated circuits are memory devices. These electronic modules are generally configured with ever-increasingly sophisticated integrated circuits and devices which require still-increasing interface demands for the connection systems.
An electronic module typically includes a printed circuit board configured as a rigid substrate fabricated generally to include multiple conductive layers and having one or more integrated circuits thereon and a connection system. One typical well known board-to-board connection system includes a portion of a printed circuit board having several electrically conductive pins or contacts along one or more edges which respectively engage with a corresponding socket including corresponding contacts (e.g., metal spring contacts). The edge and socket contacts provide an electrical connection between the electronic module and a receiving motherboard.
Printed circuit boards may be utilized to form electronic modules which are commonplace within computers and other electronic systems. As stated, one form of electronic modules includes memory modules which are used to store data in portable electronic devices such as computers. Memory modules typically include at least one integrated circuit (IC) chip which may include one or more forms of memory devices. One advantage of such memory modules is their ease in insertion into and removal from the electronic device by the use of a multi-contact connection system as described above.
Memory modules have been designed to conform to specific design standards for ease in standardization between electronic device and memory module providers. One accepted standard includes a Single In-Line Memory Module (SIMM), which is a compact circuit board designed to accommodate memory chips. The SIMM was developed to provide a modular solution for the installation of memory components into a computer or other electronic system designed to receive such components. A specific SIMM, because of the standardized design, may receive all of the necessary logic signals including the requisite power and ground signals through a board-to-board connection system associated therewith.
Memory modules that include one or more memory devices may be configured in the form of (i) a SIMM, which employs a single line or row of conductive contacts on a single side of the printed circuit board of the module or may, alternatively, be configured as (ii) a Dual In-Line Memory Module (DIMM), which utilizes two lines of conductive contacts on opposing sides of the module's printed circuit board. Clearly, a DIMM can accommodate a greater number of electrical connections to an external socket than is available from a SIMM of the same relative size. As functionality and memory density increases on memory modules, the need or desire for more electrical contacts or I/O signals becomes more apparent.
FIG. 1 illustrates front and back views of a conventional DIMM 100. The DIMM 100 includes a printed circuit board 102 on which a plurality of semiconductor memory devices 104, 106 are operably coupled. Each of the sides of DIMM 100 includes a corresponding array of electric contacts 108, 110 for electrically connecting the memory devices in a receiving electronic or computer system. Each of the contacts within each of the array of electric contacts 108, 110 typically assumes a fixed pitch or spacing as defined by one or more corresponding standardization specifications. When an increased number of contacts is desired due to an increased complexity of a memory module, the contact spacing or pitch must be reduced or the printed circuit board must be enlarged to accommodate the increased number of desired conductive contacts. It should be appreciated that a physical limitation may be imposed due to manufacturing capabilities or reliability issues that may present limitations on increasing the size of a printed circuit board or reducing the pitch between contacts on the printed circuit board.
Using a conventional notebook or compact portable electronic or computer system as an example, space for electronic components may be limited. In particular, memory modules, which may already consume a significant portion of the available volume, are increasingly designed to be more complex and sophisticated. Resolving the dilemma by simply increasing the size of the available memory module is not acceptable. As memory module technologies have become more complex including, for example, an increasing number of address lines, conventional configurations, such as those supported by specific standards (e.g., DDR2 SODIMM), have become conductive contact-limited and may not support the additional interconnections required for an expanded-capability memory standard (e.g., DDR3) technologies. Additionally, memory devices supporting faster switching times may require enhanced signal conditioning techniques (e.g., improved ground return paths), which may require further improved interconnection techniques. To accommodate increased functionality, memory modules and the interconnection standards associated therewith require additional interface contacts and techniques if the overall dimensions of the memory modules are not to be significantly increased.
FIG. 2 is a cross-sectional area of an exemplary memory module configured as a DDR2 module as fitted into a receiving socket on a motherboard, in accordance with the prior art. A cross-sectional view of DIMM 100 illustrates a cross-sectional view of a printed circuit board 102 which is illustrated to include a plurality of conductive layers 112-122 separated by insulative or nonconductive layers 124-132. As illustrated, the exterior conductive layers 112, 122 respectively couple to conductive contacts 134, 136. Accordingly, the DIMM 100 is received in a socket 138 which includes socket contacts 140, 142 for providing an electrical connection between conductive contacts 134, 136 and a motherboard 144.
In one arrangement, printed circuit board 102 includes various conductive layers that may have primary configurations as power and ground layers, illustrated as enhanced-thickness conductive layers 114, 120. Additionally, printed circuit board 102 may include one or more signal layers illustrated as conductive layers 112, 116, 118, 122. As further illustrated, only the exterior conductive layers 112, 122 are available for exterior coupling with the conductive contacts 134, 136. Therefore, coupling of internal conductive layers to conductive contacts is performed through the use of vias (not shown) for coupling internal conductive layers to the accessible exterior surfaces. The fabrication of a multilayer substrate is well known and not described herein. Therefore, there is a desire to utilize a similar board design and volume while providing additional available conductive contacts for the coupling of additional signals to a receiving socket.